Utilization of polyacids having a tight molar mass distribution

ABSTRACT

The invention relates to dental materials containing at least one polyacid or at least one polyacid and at least one salt of at least one polyacid with a molar mass distribution Mw/Mn ranging from 1.0 to 1.7, whereby the polyacid has a molecular weight Mw ranging from 1,000 to 500,000.

The invention relates to the use in dental materials of polyacids or ofpolyacids together with salts of polyacids with a narrow molar massdistribution.

Polyacids have been used in dental materials since about the end of the1960s. For example, polyacrylic acid was used as ground substance inzinc polycarboxylate cements (D. C. Smith, Br. Dent. J., 125 (1968),381-384) or also in glass ionomer cements (ASPA I, Wilson and Kent,1969; DE 20 61 513 A).

While zinc polycarboxylate cements to this day are based on polyacrylicacid, the glass ionomer cements were developed further with regard tothe chemical composition of the polyacid.

For example, copolymer acids of acrylic acid and itaconic acid for usein glass ionomer cements are known from S. Crisp, B. E. Kent, B. G.Lewis, A. J. Ferner and A. D. Wilson, J. Dent. Res., 59 (1980),1055-1063. In addition, glass ionomer cements based on a copolymer ofacrylic acid and maleic acid are known from EP 0 024 056 A1.

The use of polyvinylphosphonic acid is known, for example, from EP 0 340016 A, EP 0 431 440 A, U.S. Pat. No. 5,179,135, GB 2 272 222 A and U.S.Pat. No. 5,601,640.

The use of copolymer acids of acrylic acid and vinyl-phosphonic acid isdisclosed in GB 2 291 060 A and the use of polycarboxylic acidsfunctionalized with amino acids is disclosed in U.S. Pat. No. 5,369,142.

The polyacids are usually used in dental materials, for example inpolyelectrolyte cements and especially in zinc polycarboxylate cementsand glass ionomer cements, as highly concentrated, for exampleapproximately 30 to 50%, aqueous solutions.

The overall proportion of polyacid in dental cements is frequently, onthe one hand, chosen to be as high as possible, in order to achievemaximum strength of the cured cement; on the other hand, the system hasto exhibit, on mixing and applying, the lowest possible viscosity,guaranteeing that it can be removed from its container, for example fromcapsules. A reduction in the overall content of polyacid in dentalcements is generally, and especially in reinforced glass ionomercements, accompanied by an obvious deterioration in the mechanicalstrength of the cured cement.

That is why there exists a high demand for dental cements which have areduced viscosity at a high content of polyacid.

Various starting points for the solution of this problem have inprinciple been known to date but they suffer from disadvantages.

The possibilities of inserting the polyacid in glass ionomer cements inpowder form are limited, in particular in reinforced glass ionomerfilling cements, since in the mixing operation only a very short time,for example up to a few minutes, is available for dissolution of thepolyacid in the total system.

In principle, the viscosity of a polymer in solution can be reduced byusing branched polymers. At the same molecular weight, the solutionviscosity of polymers generally becomes smaller as the degree ofbranching increases. That is why liquid cements of low viscosity can beprepared by use of short-chain branched, long-chain branched, comb-likebranched, star-shaped, hyperbranched or dendrimeric polyacids, whichliquid cements favorably influence the overall viscosity of the system.

The disadvantage of such polyacids is, first, the significantly higherexpenditure on synthesis and consequently the increased manufacturingcosts, especially in the manufacture of specific branching structures,and, secondly, with increasing branching, the acid groups of thepolyacid become more difficult to access, so that an undesired change inthe setting characteristic occurs. In addition, poor accessibility ofthe acid groups results in lower degrees of crosslinking andconsequently reduced strengths in the cement.

Investigations into the influence of the molar mass distribution on theproperties of polycarboxylate cements are revealed in Bull. KanagawaDent. Coll. (1990), 18(1), 29-32. The polyacids investigated exhibit apolydispersity ranging from 1.9 to 5.9. To summarize, it is explainedthat the strength of cements prepared with a poly(acrylic acid) with anaverage molecular weight of greater than 100 000 with simultaneously thesmallest possible molecular weight distribution is very good. Finally,it is emphasized that, in developments in this field, both the averagemolecular weight and the molecular weight distribution should beconsidered.

Attempts by the Applicant Company to confirm the reproducibility of thispublication have revealed that, e.g., the polyacid according to SampleL82 exhibits a molar mass distribution of 7.4 and not of 1.9 as stated.

The influence of the molecular weight of polyacids on the properties ofglass ionomer cements is investigated in J. Dent. Res. (1989), 58(2),89-94. The polydispersity of the polyacids investigated lies, accordingto the values cited, in the range from 1.58 to 11.50. The values wereobtained by gel permeation chromatography using polyethylene oxideequivalents as external standard.

However, it is essential, for the reproducible determination ofmolecular weights and molecular weight distributions by gel permeationchromatography, to choose a standard which exhibits the same basicchemical structure as the substance to be measured, since this has aconsiderable influence on the elution times (J. M. G. Lowie, Chemie undPhysik der synthetischen Polymere [Chemistry and Physics of SyntheticPolymers], Vieweg Verlag 1997, Chapter 9.14). It is possible, inparticular with comparatively polar polymers, such as polyacids, whichexhibit strong tendencies to form associations via hydrogen bonds, inparticular with relative measurements against standards with differentchemical structures, to obtain measurement results which are seriouslyin error.

That is why it is an object of the present invention to find polyacidswhich, while retaining the setting and physical properties of the setcements, in particular together with conventional cement powders, makepossible reduced solution viscosities of the liquid cement andconsequently improved consistencies during the mixing operation.

This object is achieved through the use of polyacids or of polyacidstogether with salts of polyacids with a molar mass distribution of [sic]Mw/Mn between 1.0 and 1.7, preferably between 1.0 and 1.5, particularlypreferably between 1.0 and 1.3, in dental materials or the preparationof dental materials comprising polyacids with such a molar massdistribution.

The term “Mw” is to be understood, within the meaning of thisapplication, as the weight-average molecular weight determined by meansof aqueous gel permeation chromatography (GPC), for which applies:${Mw} = \frac{\sum\limits_{i}{n_{i}M_{i}^{2}}}{\sum\limits_{i}{n_{i}M_{i}}}$in which n_(i)=number of the polymer chains and M_(i)=molar mass of thepolymer chain.

The term “Mn” is to be understood, within the meaning of thisapplication, as the number-average molecular weight determined by meansof aqueous GPC, for which applies:${Mn} = {\frac{\sum\limits_{i}{n_{i}M_{i}}}{\sum\limits_{i}n_{i}} = \frac{\sum\limits_{i}{n_{i}M_{i}}}{n}}$in which n=total number of the polymer chains in a sample.

The term “dental materials” is to be understood, within the framework ofthis application, as in particular cements, such as zinc polycarboxylatecements, glass ionomer cements or resin-modified glass ionomer cements,and compomers, provided that they can be formulated with aqueouspolyacid solutions. The dental materials are curable materials, i.e.materials which in accordance with the requirements change in a periodof time of 30 sec to 30 min, preferably of 2 min to 10 min, from aviscous to a nonviscous condition.

The curing reaction can; for example, be brought about by a cementreaction, a crosslinking reaction and/or a polymerization reaction.

A viscous condition, in contrast to a nonviscous condition, in the abovemeaning then exists if the material can be processed or applied withapplication devices familiar to dentists, such as a spatula, syringe ormixing capsule.

The term “polyacids” is to be understood as meaning polymers andcopolymers which exhibit more than three acid groups per polymermolecule. The polymers or copolymers can in addition also exhibit otherfunctional groups. Polyacids according to the present invention are notto be understood as individual substances but as mixtures of the mostvaried individual molecules which in each case exhibit varying molarmasses.

The term “acid groups” is to be understood as meaning in particularcarboxylic acid groups, phosphonic acid groups, phosphoric acid groupsor sulfonic acid groups.

The terms “to include” and “to comprise” within the meaning of thepresent invention introduce an enumeration of characteristics which isnot comprehensive. The expression “one” is equivalent to the statementof “at least one”.

The polyacids used according to the invention exhibit a molar mass Mwranging from 1 000 to 500 000, preferably ranging from 2 000 to 100 000,particularly preferably ranging from 5 000 to 80 000.

Polyacids exhibiting the molar mass distribution according to theinvention have, for example, at a concentration of 38 to 47% in water, aviscosity of 0.49 to 4.23 Pa.s, preferably, at a concentration of 42 to46% in water, a viscosity of 1.55 to 3.11 Pa.s, the viscosity beingdetermined with a PK100 (Haake) viscometer at 23° C.

The fact that the object described is achieved with the molar massdistribution according to the invention is surprising because, accordingto previous information, the high molar masses of a polyacid with abroad distribution were regarded as essential for cement strengths (H.J. Posser et al., J. Dent. Res., 1986, and J. Dent. (1977), 5(2),117-20), while the low molar masses drastically reduce the viscosity ofthe polyacid solution (H. G. Elias, Makromoleküle [Macromolecules],Volume 1, Hüthing & Wepf Verlag).

The disadvantages relating back to branchings, such as pooraccessibility of the acid groups, are avoided in a particularly simpleway by the use of unbranched polyacids with a narrow molar massdistribution.

The polyacids which can be used according to the invention preferablyexhibit repeat units of the formula (1) occurring either as sole repeatunits or with additional repeat units, the repeat units in copolymersbeing able to be randomly or alternately arranged along the main polymerchain:—CR¹R²—CR³R⁴—  (1)

-   -   C=carbon;    -   R¹═COOH, PO₃H₂, OPO₃H₂, SO₃H₂;    -   R²═H, CH₃, C₂H₅ or CH₂COOH;    -   R³═H;    -   R⁴═H, COOH, COOR⁵, in which R⁵ is taken from the following        group: linear, branched or cyclic alkyl residue with 1 to 12 C        atoms, preferably CH₃, C₂H₅, C₃H₇, C₄H₉; substituted or        unsubstituted aryl residue with 6 to 18 C atoms, preferably        phenyl or benzyl; linear, branched or cyclic alkyl residue with        1 to 12 C atoms functionalized with 1 to 5 heteroatoms from the        group consisting of N, O and S, preferably CH₃O, C₂H₄OR⁶, in        which R⁶ represents an acyl residue, preferably acryl or        methacryl.

Preferred representatives of formula (1) are:

-   -   1. Polyacrylic acid    -   2. Copolymers of polyacrylic acid with more than 30 mol %,        preferably more than 50 mol %, of acrylic acid units;    -   3. Polymers and copolymers with more than 30 mol %, preferably        more than 50 mol %, of units from the group: maleic acid,        methacrylic acid, fumaric acid, itaconic acid, vinylphosphonic        acid, vinylidenediphosphonic acid, vinylsulfonic acid or vinyl        phosphate.

Comonomers for this are preferably taken from the group: methacrylicacid, maleic acid, maleic anhydride, fumaric acid, itaconic acid,itaconic anhydride, glutaconic acid, citridic acid, citraconic acid,methaconic [sic] acid, tiglic acid, crotonic acid, muconic acid,isocrotonic acid, 3-butenoic acid, cinnamic acid, styrenecarboxylicacid, vinylphthalic acid, abietinic acid, styrenesulfonic acid,styrene-phosphonic acid, 1-phenylvinylphosphonic acid, vinylphosphonicacid, vinylidenediphosphonic acid, vinylsulfonic acid, vinyl phosphate,other monomers with acid functional groups and substituted derivativesthereof, especially esters or amides or imides of the acids mentionedwith up to 10 C atoms in the alkoxide or amine or imine residue,preferably acrylic esters, methacrylic esters, maleic esters orcorresponding amides or imides, for example maleimide, for examplemethyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate,n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate,N-methylmaleimide, N-ethylmaleimide, acrylamide, N-methylacrylamide,N,N-dimethylacrylamide, N-ethylacrylamide, 2-hydroxyethyl acrylate,2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate or 3-hydroxypropylmethacrylate.

Other comonomers, additionally or exclusively, can also be included, forexample ethylene, butadiene or isoprene.

The comonomers can be incorporated randomly or alternately, preferablyrandomly.

Preference is likewise given to partially saponified polyacrylic esters,in particular poly(acrylic acid-co-methyl acrylate), poly(acrylicacid-co-ethyl acrylate), poly(acrylic acid-co-propyl acrylate), in whichthe propyl residue can be either linear or branched, poly(acrylicacid-co-butyl acrylate [sic], in which the butyl residue can be linearor branched, poly(acrylic acid-co-phenyl acrylate), poly(acrylicacid-co-benzyl acrylate), in each case with an incorporation ratio ofthe comonomers of 1:1 000 to 1 000:1.

It is common to the polyacids used according to the state of the artthat they are prepared by means of conventional radical polymerization.In the course of this, materials are inevitably formed having a broadmolar mass distribution with Mw/Mn very much greater than 1.7, generallyapproximately 4 to 6.

Polyacids according to the present invention displaying the molar massdistributions according to the invention can preferably be prepared viaanionic polymerization, group transfer polymerization or controlledradical polymerization.

Suitable methods are described in more detail below:

A possible synthesis is carried out via the esters of polyacids, theacids with the molar mass distribution according to the invention beingobtained by living anionic or group transfer polymerization of thecorresponding monomers and subsequent polymer-analogous saponificationof the ester groups.

The term “polymer-analogous reactions” is to be understood, within themeaning of this invention, as generally reactions on the polymer whileretaining the degree of polymerization.

For example, esters of polyacrylic acid, such as tert-butyl ester,n-butyl ester, benzyl ester or trimethyl-silyl ester, can be polymerizedand subsequently the ester groups can be saponified in apolymer-analogous way, as is described in S. P. Rannard et al., Eur.Polym. J., 29, 407-414 (1993), or in Y. Morishima et al., Macromol.Chem., Rapid Commun., 2, 507-510 (1981). Polyacids with the molar massdistribution according to the invention can be obtained as well throughthe use of controlled radical polymerization. Polymerization methodsbased on the following systems are suitable:

-   -   N-oxyl radical initiator systems, as described in A. Goto and T.        Fukuda, Macromolecules, 1999, 32, 618-623, or Keoshkerian et        al., Macromolecules, 1998, 31, 7559-7561;    -   metal complex/halide systems, as described in K. Matyjaszewski        et al., Macromol. Rapid Commun., 20, 341-346 (1999).

Additional applicable methods are reverse atom transfer radicalpolymerization, as described in G. Moineau et al., Macromolecules, 1998,31, 545-547, and reversible addition-fragmentation chain transfer (RAFTmethod), as described in Y. K. Chong et al., Macromolecules, 1999, 32,2071-2074.

The saponification of polyacid esters is possible according toconventional methods (Houben-Weyl, Methoden der organischen Chemie),without the narrow molar mass distribution changing. Methyl, benzyl ortert-butyl esters, for example, are especially easy to cleave and forthis reason are preferred.

Polyacids with the molar mass distribution according to the invention,in the simplest case polyacrylic acid, show, with carboxylate cementsand glass ionomer cements, identical strengths with only 25 to 30% ofthe solution viscosity. The number-average molar masses Mn are in thiscase comparable with those of conventional polyacids with a broaddistribution from dental materials, for example polyacrylic acid.

Curable dental materials or cements can be prepared with the polyacidsdescribed, which dental materials or cements have a compressive strengthranging from 220 to 250 MPa (measured according to ISO 9917), a bendingstrength ranging from 35 to 45 MPa (measured analogously to ISO 4049with test specimens 12 mm long) and/or a surface hardness ranging from400 to 500 MPa (measured according to DIN 53456).

Powder/liquid ratios which can be used for curable dental materialsaccording to the invention obtainable by mixing a powder with a liquidrange from 0.7 to 6.0, preferably from 1.0 to 5.0, particularlypreferably from 1.5 to 3.5.

With the number-average molar mass Mn, the polymer chains of varyinglengths are weighted in accordance with their number in the averaging(Lehrbücher der Polymerchemie [Manuals of Polymer Chemistry], forexample H. G. Elias, Makromoleküle [Macromolecules], Volume 1, Hüthing &Wepf-Verlag).

The cations of the salts of the polyacids which can be used according tothe invention are taken from the group: alkali metal elements, alkalineearth metal elements, zinc, aluminum, scandium, yttrium or lanthanum.Na, Ca and Al salts are preferred in this connection.

The polyacids described in the framework of this invention are used indental materials in order, in comparison with dental materials from thestate of the art, in which polyacids with a high value of the molar massdistribution are used, to make possible a decrease in the viscositywhile retaining the physical parameters of the cured dental material. Inparticular, the compressive strength and the bending strength, inaddition to the surface hardness, are not reduced, in many cases areeven improved, and the viscosity of the mixed dental material is reducedbefore the beginning of the curing.

The polyacids or salts of polyacids, provided that they are sufficientlysoluble, can, according to the field of application, be used as liquidor as solid, for example obtained through freeze drying or spray drying.

Preferred dental materials in the framework of this invention are eitherformulated with a single component, such as compomers, or with two ormore components, such as carboxylate cements, glass ionomer cements andresin-modified glass ionomer cements, in which the liquid components arestored separately from the solid components and are mixed immediatelybefore application.

Particular preference is given to cements which, in the case of glassionomer cements, for example, can include the following constituents:

-   -   (A) 1 to 60% by weight, preferably 5 to 40% by weight,        particularly preferably 10 to 30% by weight, of polyacids or        polyacids together with salts of polyacids with the molar mass        distribution according to the invention;    -   (B) 35 to 80% by weight, preferably 50 to 70% by weight, of        fillers;    -   (C) 0 to 20% by weight, preferably 1 to 10% by weight, of        additives and auxiliaries;    -   (D) 5 to 40% by weight, preferably 9 to 30% by weight, of water.

The term “fillers” of the component (B) is to be understood as mainlyreactive or nonreactive solids.

Suitable examples are reactive fluoroaluminosilicate glasses from DE 2061 513 A1, DE 20 65 824 A1, or reactive glasses which, on the surface,in comparison with the average composition, are depleted in calciumions, as described in DE 29 29 121 A1.

The last-named glasses are especially preferred and can exhibit thefollowing composition: Constituent Calculated as % by weight Si SiO₂ 20to 60 Al Al₂O₃ 10 to 50 Ca CaO  1 to 40 F F  1 to 40 Na Na₂O  0 to 10 PP₂O₅  0 to 10and a total of 0 to 20% by weight, calculated as oxides, of B, Bi, Zn,Mg, Sn, Ti, Zr, La or other trivalent lanthanides, K, W, Ge, and otheradditives, which do not impair the properties and are physiologicallycompletely harmless.

In addition to the reactive glasses described above, inert fillers, suchas quartz, can be used.

The term “component (C)” is to be understood as, for example, additivesfor accelerating and improving the curing, as are known from DE 2 319715 A1. Preferably, chelating agents in the form of low molecular weightacid molecules, such as tartaric acid, are added.

Coloring pigments and other auxiliaries usual in the field of glassionomer cements, for example for improving the miscibility, are also tobe understood under “component (C)”.

Apart from their use in conventional glass ionomer cements, thepolyacids with the molar mass distribution according to the inventionare also suitable for use in carboxylate cements.

In this connection, the compositions include, for example, the followingconstituents:

-   -   (A) 1 to 60% by weight, preferably 5 to 40% by weight,        particularly preferably 10 to 30% by weight, of polyacids or        polyacids together with salts of polyacids with the molar mass        distribution according to the invention;    -   (C) 0 to 20% by weight, preferably 1 to 10% by weight, of        additives and auxiliaries;    -   (D) 10 to 40% by weight, preferably 15 to 30% by weight, of        water;    -   (E) 30 to 80% by weight, preferably 44 to 70% by weight, of zinc        oxide.

Compomers or resin-modified glass ionomer cements comprising thepolyacids with the molar mass distribution according to the inventioninclude, for example, the following components:

-   -   (A) 1 to 75% by weight, preferably 2 to 69.9% by weight,        particularly preferably 10 to 30% by weight, of polyacids or        polyacids together with salts of polyacids with the molar mass        distribution according to the invention;    -   (D) 5 to 40% by weight, preferably 10 to 30% by weight, of        water;    -   (F) 8.9 to 70% by weight, preferably 10 to 60% by weight, of one        or more radically polymerizable monomers;    -   (G) 10 to 90% by weight, preferably 15 to 87.9% by weight, of        fillers;    -   (H) 0.1 to 5% by weight, preferably 0.5 to 3% by weight, of        initiators and optionally activators;    -   (I) 0 to 30% by weight, preferably 0.1 to 20% by weight, of        additives, optionally pigments, thixotropic agents,        plasticizers.

Mono-, di- or polyfunctional ethylenically unsaturated compounds,preferably based on acrylate and/or methacrylate, are used as component(F). These can comprise both monomeric and polymolecular oligomeric orpolymeric acrylates. In addition, they can be used in the formulationsalone or as mixtures.

Suitable monomers are, for example, the acrylic and methacrylic estersof mono-, di- or polyfunctional alcohols. The following are mentioned asexamples: 2-hydroxyethyl (meth)acrylate, methyl (meth)acrylate, isobutyl(meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycoldi(meth)acrylate (TEGDMA), hexanediol di(meth)acrylate, dodecanedioldi(meth)acrylate and trimethylolpropane tri(meth)acrylate.

Others which can advantageously be used are bisphenol A di(meth)acrylateand the ethoxylated or propoxylated di(meth)acrylates derived therefrom.In addition, the monomers described in U.S. Pat. No. 3,066,112 A, basedon bisphenol A (meth)acrylate and glycidyl (meth)acrylate or theirderivatives arising from addition of isocyanates, are suitable.

The diacrylic and dimethacrylic esters ofbis(hydroxy-methyl)tricyclo[5.2.1.0^(2,6)] decane mentioned in DE 28 16823 C1 and the diacrylic and dimethacrylic esters of the compounds ofbis(hydroxy-methyl)tricyclo[5.2.1.0^(2,6)] decane extended with 1 to 3ethylene oxide and/or propylene oxide units are also especiallysuitable.

Urethane (meth)acrylates, such as7,7,9-trimethyl-4,13-dioxo-5,12-diazahexadecane-1,16-dioxy [sic]dimethacrylate (UDMA), can also be a constituent of this component.

Fillers according to component (G) can be inorganic fillers, for examplequartz, glass powder, water-insoluble fluorides, such as CaF₂, silicagels and silicic acid, especially pyrogenic silica gel, and theirgranulates. Cristobalite, calcium silicate, zirconium silicate,zeolites, including molecular sieves, metal oxide powders, such asaluminum or zinc oxides or their mixed oxides, barium sulfate, yttriumfluoride or calcium carbonate can also be used as fillers.

Fluoride-releasing fillers, for example complex inorganic fluorides ofthe general formula A_(n)MF_(m), as described in DE 44 45 266 A1, canalso be used or added. A represents a mono- or polyvalent cation, Mrepresents a metal from the main group or subgroup III, IV or V, nrepresents an integer from 1 to 3 and m represents an integer from 4 to6.

Organic fillers can also be a constituent of this component.

Those mentioned by way of example are conventional pearl-shaped polymersand copolymers based on methyl methacrylate, which, for example, areavailable from Röhm under the name “Plexidon” or “Plex”.

For improved incorporation in the polymer matrix, it can be advantageousto render hydrophobic, using a silane, the fillers mentioned andoptionally additives opaque to X-rays. The amount of the silane usedusually amounts to 0.5 to 10% by weight, with reference to inorganicfillers, preferably 1 to 6% by weight, very particularly preferably 2 to5% by weight, with reference to inorganic fillers. Normal hydrophobingagents are silanes, for example trimethoxymethacryl-oxypropylsilane[sic].

The maximum mean particle size of the preferably inorganic fillersusually amounts to 15 μm, in particular 8 μm. Fillers with a meanparticle size of <3 μm are very particularly preferably used.

The term “initiators” according to component (H) is to be understood asinitiator systems which bring about the radical polymerization ofmonomers, for example photoinitiators and/or what are known as redoxinitiator systems and/or thermal initiators.

Examples of suitable photoinitiators are α-diketones, such ascamphorquinone, in conjunction with secondary and tertiary amines, ormono- and bisacylphosphine oxides, such as2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,6-dichlorobenzoyl) (4-n-propylphenyl)-phosphine oxide. However, othercompounds of this type, as are described in EP 0 073 413 A1, EP 0 007508 A1, EP 0 047 902 A1, EP 0 057 474 A1 and EP 0 184 095 A1, are alsosuitable.

Organic peroxide compounds together with “activators” are suitable asredox initiator systems. Compounds such as lauroyl peroxide, benzoylperoxide, p-chlorobenzoyl peroxide and p-methylbenzoyl peroxide aresuitable in particular as organic peroxide compounds.

Tertiary aromatic amines, such as theN,N-bis(hydroxyalkyl)-3,5-xylidines known from U.S. Pat. No. 3,541,068,and the N,N-bis(hydroxyalkyl)-3,5-di(tert-butyl)anilines known from DE26 58 530 A1, especiallyN,N-bis(β-hydroxybutyl)-3,5-di(tert-butyl)aniline, andN,N-bis(hydroxyalkyl)-3,4,5-trimethylanilines, for example, are suitableas activators.

Highly suitable activators are also the barbituric acids and barbituricacid derivatives described in DE 14 95 520 A1 and the malonyl sulfamidesdescribed in EP 0 059 451 A1. Preferred malonyl sulfamides are2,6-dimethyl-4-isobutylmalonyl sulfamide, 2,6-diisobutyl-4-propylmalonylsulfamide, 2,6-dibutyl-4-propylmalonyl sulfamide,2,6-dimethyl-4-ethylmalonyl sulfamide and 2,6-dioctyl-4-isobutylmalonylsulfamide.

For further acceleration, the polymerization is in this connectionpreferably carried out in the presence of heavy metal compounds andionogenic halogen or pseudo-halogen. Copper is especially suitable asheavy metal and the chloride ion is especially suitable as halide. Theheavy metal is suitably used in the form of soluble organic compounds.Likewise, the halide and pseudohalide ions are suitably used in the formof soluble salts, examples which may be mentioned being the solubleamine hydrochlorides and quaternary ammonium chloride compounds.

If the dental materials according to the invention comprise a redoxinitiator system formed from organic peroxide and activator, peroxideand activator are then preferably present in parts of the dentalmaterial according to the invention which are spatially separate fromone another, and they are homogeneously mixed with one another onlyimmediately before use. If organic peroxide, copper compound, halide andmalonyl sulfamide and/or barbituric acid are present side by side, thenit is particularly sensible for the organic peroxide, malonyl sulfamideand/or barbituric acid and the copper compound/halide combination to bepresent in three constituents spatially separate from one another. Forexample, the copper compound/halide combination, polymerizable monomersand fillers can be kneaded to a paste and the other components can bekneaded to two separate pastes in the above-described way in each casewith a small amount of fillers or in particular thixotropic agents, suchas silanized silicic acid, and a plasticizer, for example phthalate. Onthe other hand, the polymerizable monomers can also be present togetherwith organic peroxide and fillers. Alternatively, organic peroxide,copper compound, halide and malonyl sulfamide and/or barbituric acid canalso be split up according to DE 199 28 238 A1.

Soluble organic polymers can be used as representatives of component(I), for example for increasing the flexibility of the materials.Poly(vinyl acetate) and the copolymers based on vinyl chloride/vinylacetate, vinyl chloride/vinyl isobutyl ether and vinyl acetate/maleicacid dibutyl ether [sic], for example, are suitable. Dibutyl, dioctyland dinonyl phthalates or adipates and polymolecular polyphthalic andadipic [sic] esters, for example, are highly suitable as additionalplasticizers. Modified layered silicates (bentonites) or organicmodifying agents, for example based on hydrogenated castor oils, canalso be used, in addition to pyrogenic silicic acids, as thixotropicagents. Furthermore, inhibitors, as are described in EP 0 374 824 A1 ascomponent (d), can be included in the formulations as additives.

Furthermore, containers which include dental materials comprisingpolyacids or polyacids together with salts of polyacids with a molarmass distribution according to the invention, for example capsules,blister packs, application syringes or cannulas, are a subject matter ofthis invention.

The invention is subsequently illustrated by means of examples, withoutit being limited in any way thereby. The determination of the molar massdistribution was carried out in this connection via aqueous gelpermeation chromatography (GPC) at pH=7 against polyacrylic acid sodiumsalt standard with the RID6a refractive index detector (Shimadzu).Polyacrylic acid sodium salt standards (PSS) were used for calibration.The measured values were converted to free polyacrylic acid using thefactor 0.766. The measurement was carried out at 23° C.

The samples were measured here as 0.05% aqueous solutions in thesolvent, a 0.9% by weight aqueous sodium nitrate solution, to which 200ppm of sodium azide are also added. The solutions were adjusted to pH=7by addition of sodium hydroxide.

A column combination of Hema3000, HemaBio1000 and HemaBio40 (PSS) wasused to measure maximum molecular weights of up to 670 000 g/mol. Acolumn combination of Suprema1000, Hema3000 and HemaBio1000 (PSS) wasused with maximum molecular weights of up to 1 100 000 g/mol.

SYNTHETIC EXAMPLE 1 Preparation of a Polyacrylic Acid (a)

A mixture of 0.65 g of methyl 2-bromopropionate, 0.28 g of copper(I)bromide, 0.02 g of copper(II) bromide, 0.35 g ofN,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) and 100 g oftert-butyl acrylate was dissolved in 100 ml of dimethylformamide in areaction flask under an argon atmosphere and was heated to 70° C. Thepolymerization reaction was monitored using ¹H NMR spectroscopy. After24 hours, the preparation was virtually completely polymerized.

After dissolving the mixture in 500 ml of toluene, washing was carriedout with dilute hydrochloric acid and with water, and the organic phasewas subsequently concentrated.

The polymer obtained was, in order to cleave the ester groups, dissolvedin 500 ml of dioxane and heated for five hours at 100° C. with an excessof concentrated hydrochloric acid. Dioxane and hydrochloric acid wereremoved by repeated extraction with diethyl ether, concentration on arotary evaporator, finally with addition of water. The polyacrylic acidwas obtained as a colorless aqueous solution which was adjusted to theconcentrations given in table 1 (according to titration with lithiumhydroxide in the presence of 1% lithium chloride).

SYNTHETIC EXAMPLE 2 Preparation of a Polyacrylic Acid (b)

A mixture of 1.22 g of methyl 2-bromopropionate, 0.102 g of copper(I)bromide, 0.250 g of PMDETA and 87 g of methyl acrylate was heated to 80°C. in a reaction flask under an argon atmosphere. After 15 hours, thepreparation was virtually completely polymerized. The preparation wasdissolved in 500 ml of toluene and extracted with dilute hydrochloricacid and with water. The organic phase was concentrated.

The product was dissolved in 500 ml of dioxane and treated with 100 mlof 4N potassium hydroxide solution. Ester saponification was completeafter heating at 80° C. for five hours. The lumpy mixture was dilutedwith water and treated with an acidic ion exchanger. Repeated extractionwith diethyl ether and concentration under vacuum with addition of watergave a yellow-colored aqueous solution of the polyacrylic acid.

The determination of the molar mass distribution was carried out viaaqueous GPC at pH=7 against polyacrylic acid sodium salt standard.

SYNTHETIC EXAMPLE 3 Preparation of Poly(Acrylic Acid-co-butyl Acrylate)(c)

89.8 g of n-butyl acrylate, 0.288 g of2,2,6,6-tetramethyl-1-(α-phenethoxy)piperidine (TEMPEP), 0.64 g ofα-D-(+)-glucose and 0.64 g of sodium hydrogen-carbonate were mixedtogether in a reaction flask under an argon atmosphere and were heatedat 145° C. for five hours, during which a polymerization conversion of40% was achieved. The preparation was concentrated under vacuum andextracted several times with methanol. The polymer was obtained as acolorless oil.

For partial saponification, 16.4 g of the poly(butyl acrylate) weredissolved in 160 ml of ethanol and were treated with 10 ml of water and10.4 g of sodium hydroxide. The preparation was stirred at 50° C. for 24hours, during which several portions of water were added in order toprevent precipitation of the polymer. The reaction conversion was 96%.

The reaction solution was diluted with water and treated with an acidicion exchanger. Extraction was subsequently carried out with diethylether and the aqueous phase was concentrated on a rotary evaporator. Aslightly yellowish, aqueous solution of the poly(acrylic acid-co-butylacrylate) with an incorporation ratio of 96:4 in favor of acrylic acid(¹H NMR) was obtained.

The determination of the molar mass distribution was carried out viaaqueous GPC at pH=7.

SYNTHETIC EXAMPLE 4 Preparation of the Sodium Salt of Polyacrylic Acid(a) [sic]

80 g of a 40% aqueous solution of the polyacrylic acid according tosynthetic example 1 are treated with a solution of 17.8 g (1 equivalent)of sodium hydroxide in 50 ml of water with stirring and cooling. Thepreparation is stirred at ambient temperature for a further 3 hours andis subsequently concentrated to dryness on a rotary evaporator. The saltof the polymer is ground up in a mortar and is dried at 110° C. in adrying oven to constant weight.

SYNTHETIC EXAMPLE 5 Preparation of the Sodium Salt of Polyacrylic Acid(e)

The synthesis was carried out analogously to synthetic example 2 [sic].

The determination of the molar mass distribution was carried out viaaqueous GPC at pH=7 against polyacrylic acid sodium salt standard.

USE EXAMPLES

The polyacids according to the preparation examples were tested in theapplication for dental carboxylate cements and glass ionomer cements.

The procedure used to determine the compressive strengths of the setcements was that of the ISO 9917 standard. Bending strengths weredetermined using the ISO 4049 standard, in which, however, testspecimens with a length of 12 mm were used. Both the measurement ofcompressive strengths and that of bending strengths were in each casecarried out on a series of 5 test specimens, in which the relative errorwas approximately ±10% per measured value. Surface hardnesses weredetermined according to DIN 53456.

The viscosities of the aqueous polyacid solutions were measured with aPK 100 viscometer from Haake at 23° C.

Concentrations were determined by titration with lithium hydroxide inthe presence of 1% by weight of lithium chloride.

The stated polyacids were spatulated either with the powder part of thecarboxylate cement Durelon® (ESPE Dental AG, Seefeld, Germany),including more than 90% by weight of zinc oxide, or a standard glassionomer powder based on a calcium strontium fluoroaluminosilicate glass(glass ionomer cement glass) (Diamond Carve Powder, Kemdent, England).In each case, the liquid of the product Durelon® already mentionedabove, a polyacid with a molar mass distribution Mw/Mn=5.0, was used ascomparative example. The results are summarized in table 2. TABLE 1Properties of the polyacids with a molar mass distribution according tothe invention and of the comparative example Concentration ViscosityPolyacid [%] [Pa · s] Mn Mw/Mn Comparison 42 8.13 12 000 5.0 (a) 40 0.5713 000 1.1 42 1.55 45 2.68 47 3.79 (b) 38 0.49 12 500 1.5 42 1.72 442.58 47 4.23 (c) 46 3.11 16 000 1.3 (d) 41 1.98 15 100 1.4 (e) 38 2.7360 000 1.2

The viscosity of the polyacids exhibiting the molar mass distributionsaccording to the invention is, at comparable concentration andcomparable number-average molecular weight Mn, lower than that of thecomparative example. TABLE 2 Strength values of the use examples Concen-Powder/ Compressive Bending tration Powder liquid strength strengthPolyacid [%] component ratio [MPa] [MPa] (a) 42 Durelon 1.5 70 (a) 42Durelon 2.5 97 Comparison 42 Durelon 1.5 75 Comparison 42 Durelon 2.5 95(a) 42 GIC glass 3.5 240 43 Comparison 42 GIC glass 3.5 237 42 (b) 42Durelon 1.5 72 (b) 42 Durelon 2.5 96 (b) 42 GIC glass 3.5 243 41Comparison 42 Durelon 1.5 75 Comparison 42 Durelon 2.5 95 Comparison 42GIC glass 3.5 237 42 (e) 38 GIC glass 3.5 232 42 (c) 46 Durelon 1.5 74(c) 46 GIC glass 3.5 246 44 Comparison 46 Durelon 1.5 (*) Comparison 46GIC glass 3.5GIC = glass ionomer cement(*) The viscosity of the comparative polyacid is too high for suitabletest specimens to be prepared.

The strength values of the dental materials including polyacids with amolar mass distribution according to the invention lie in the same rangeas the values of the comparative materials.

The surface hardnesses of the dental materials according to theinvention, when glass ionomer cement glass is used, lie in the rangefrom 400 to 500 MPa and consequently at the same level as when thecomparative polyacid is used.

To summarize, polyacids with a molar mass distribution according to theinvention make possible the formulation of dental materials of reducedviscosity with, in comparison with materials of the state of the art,unchanged strength values.

1-10. (canceled)
 11. A curable dental material, comprising: at least onepolyacid, or at least one polyacid with at least one salt of at leastone polyacid wherein the at least one polyacid or at least one polyacidwith at least one salt of at least one polyacid has a molar massdistribution Mw/Mn between 1.0 and 1.7, wherein the at least onepolyacid or at least one polyacid with at least one salt of at least onepolyacid has a molecular weight Mw ranging from 1,000 to 500,000,wherein the at least one polyacid or at least one polyacid with at leastone polyacid salt is optionally prepared via at least one of anionicpolymerization, group transfer polymerization, and controlled radicalpolymerization.
 12. The curable dental material as claimed in claim 11,wherein said at least one polyacid or at least one polyacid with atleast one salt of at least one polyacid is linear, unbranched, andnoncrosslinked.
 13. The curable dental material as claimed in claim 11,wherein said a molar mass distribution Mw/Mn is between 1.0 and 1.5. 14.The curable dental material as claimed in claim 11, wherein said a molarmass distribution Mw/Mn is between 1.0 and 1.3.
 15. The curable dentalmaterial as claimed in claim 11, wherein the polyacid or polyacid saltcomprises repeat units of formula (1), wherein the repeat units occureither as sole repeat units, or with optional additional repeat units toform a copolymer, and the repeat units in the copolymer are randomly oralternately arranged along a main polymer chain:—CR^(I)R²—CR³R⁴—  (1) wherein C=carbon; R¹═COOH, PO₃H₂, OPO₃H₂, orSO₃H₂; R²═H, CH₃, C₂H₅, or CH₂COOH; R³═H; and R⁴═H, COOH, or COOR⁵ inwhich R⁵ is selected from the group consisting of: linear, branched, orcyclic alkyl residues with 1 to 12 C atoms; substituted or unsubstitutedaryl residues with 6 to 18 C atoms; linear, branched or cyclic alkylresidues with 1 to 12 C atoms, wherein at least one C atom isfunctionalized with 1 to 5 heteroatoms selected from the groupconsisting of N, O, and S.
 16. The curable dental material as claimed inclaim 15, wherein R⁴ is at least one of CH₃O and C₂H₄OR⁶, wherein R⁶ isan acyl residue.
 17. The curable dental material as claimed in claim 16,wherein R⁶ is acryl or methacryl.
 18. The curable dental material asclaimed in claim 11, wherein the polyacid is at least one of:polyacrylic acid; poly(acrylic acid-alt-maleic acid); poly(acrylicacid-co-maleic acid) with an incorporation ratio of the comonomers of1:1,000 to 1,000:1; poly(acrylic acid-co-itaconic acid) with anincorporation ratio of the comonomers of 1:1,000 to 1,000:1;poly(acrylic acid-co-fumaric acid) with an incorporation ratio of thecomonomers of 1:1,000 to 1,000:1; and partially saponified polyacrylicesters.
 19. A curable dental material, comprising: (A) 1 to 60% byweight of at least one polyacid or at least one polyacid and salt of atleast one polyacid, wherein the at least one polyacid or at least onepolyacid and salt of at least one polyacid have a molar massdistribution Mw/Mn between 1.0 and 1.7; (B) 35 to 80% by weight of atleast one filler; (C) 0 to 20% by weight of at least one of an additiveand an auxiliary; and (D) 5 to 40% by weight of water, wherein thepolyacid is optionally prepared via at least one of anionicpolymerization, group transfer polymerization, and controlled radicalpolymerization.
 20. A curable dental material, comprising: (A) 1 to 60%by weight of polyacids or polyacids and salts of polyacids with a molarmass distribution Mw/Mn between 1.0 and 1.7; (C) 0 to 20% by weight ofat least one of an additive and an auxiliary; (D) 10 to 40% by weight ofwater; and (E) 30 to 80% by weight of zinc oxide; wherein the polyacidis optionally prepared via at least one of anionic polymerization, grouptransfer polymerization, and controlled radical polymerization.
 21. Thecurable dental material as claimed in claim 20 wherein said a molar massdistribution Mw/Mn is between 1.0 and 1.5.
 22. The curable dentalmaterial as claimed in claim 20, wherein said a molar mass distributionMw/Mn is between 1.0 and 1.3.
 23. A curable dental material, comprising:(A) 1 to 75% by weight of at least one polyacid or at least one polyacidand salt of at least one polyacid with a molar mass distribution Mw/Mnbetween 1.0 and 1.7; (D) 5 to 40% by weight of water; (F) 8.9 to 70% byweight of at least one radically polymerizable monomer; (G) 10 to 90% byweight of at least one filler; (H) 0.1 to 5% by weight of at least oneinitiator and optionally at least one activator; and (I) 0 to 30% byweight of at least one additive; wherein the polyacid is optionallyprepared via at least one of anionic polymerization, group transferpolymerization, and controlled radical polymerization.
 24. The curabledental material as claimed in claim 23, wherein the additive comprisesat least one of a pigment, a thixotropic agent, and a plasticizer.
 25. Amethod of treating a patient in need of dental material, comprisingproviding to a patient in need thereof a sufficient amount of a curabledental material, wherein the curable dental material comprises at leastone polyacid or at least one polyacid and at least one salt of at leastone polyacid wherein the at least one polyacid or at least one polyacidwith at least one salt of at least one polyacid has a molar massdistribution Mw/Mn between 1.0 and 1.7, wherein the polyacid isoptionally prepared via at least one of anionic polymerization, grouptransfer polymerization, and controlled radical polymerization; andcuring said dental material.
 26. A kit, comprising at least one curabledental material, wherein the dental material comprises at least onepolyacid or at least one polyacid and at least one salt of at least onepolyacid wherein said at least one polyacid or at least one polyacidwith at least one salt of at least one polyacid has a molar massdistribution Mw/Mn between 1.0 and 1.7, wherein the polyacid or polyacidwith at least one polyacid salt is optionally prepared via at least oneof anionic polymerization, group transfer polymerization, and controlledradical polymerization, and instructions for using the curable dentalmaterial.
 27. The kit as claimed in claim 26, wherein the kit furthercomprises at least one of a container and a capsule.
 28. A compositionof matter, comprising: at least one polyacid, or at least one polyacidwith at least one salt of at least one polyacid, wherein said at leastone polyacid or at least one polyacid with at least one salt of at leastone polyacid has a molar mass distribution Mw/Mn between 1.0 and 1.7,wherein the polyacid has a molecular weight Mw ranging from 1,000 to500,000.
 29. The composition of matter as claimed in claim 28, whereinthe at least one polyacid, or at least one polyacid with at least onesalt of at least one polyacid, is linear, unbranched, andnoncrosslinked.
 30. A method of preparing a composition of matter,comprising: preparing at least one polyacid, or at least one polyacidwith at least one polyacid salt via at least one of anionicpolymerization, group transfer polymerization, and controlled radicalpolymerization; obtaining at least one polyacid or at least one polyacidwith at least one salt of at least one polyacid with a molar massdistribution Mw/Mn between 1.0 and 1.7, and a molecular weight Mwranging from 1,000 to 500,000.
 31. A method of preparing a curabledental material, comprising: preparing at least one polyacid, or atleast one polyacid with at least one polyacid salt via at least one ofanionic polymerization, group transfer polymerization, and controlledradical polymerization; obtaining at least one polyacid or at least onepolyacid with at least one salt of at least one polyacid with a molarmass distribution Mw/Mn between 1.0 and 1.7, and a molecular weight Mwranging from 1,000 to 500,000; combining the at least one polyacid, orat least one polyacid with at least one polyacid salt, with water, afiller, optionally an additive, and optionally an auxilliary.